Optimal Propulsion System Design for a Micro Quad Rotor
Harrington, Aaron Michael
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Currently a 50 gram micro quad rotor vehicle is being developed in collaboration with Daedalus Flight Systems. Optimization of the design at this scale requires a systematic study to be carried out to investigate the factors that affect the vehicles performance. Endurance of hovering vehicles at this scale is severely limited by the low efficiencies of their propulsion systems and rotor design and optimization has been performed in the past in an attempt to increase endurance, but proper coupling of the rotor with the motor has been lacking. The current study chose to investigate the factors that had the greatest effect on the vehicle's endurance through analysis of the propulsion system. Therefore, a coupled aerodynamic and structural analysis was carried out that incorporated low Reynolds number airfoil table lookup in order to predict micro rotor performance. A parametric study on rotor design was performed further determine the effect of different rotor designs on hover performance. The experiments performed showed that airfoil camber had the biggest impact on rotor efficiency and other factors such as leading edge shape, number of blades, max camber location, and blade planform taper only had negligible influence on performance. Systematic studies of the interactions between micro rotor blades operating in close proximity to each other were performed in order to determine the changes in rotor efficiency that might occur in a compact quad rotor design. Tests done on the effect of rotor separation demonstrated that there is a negligible interaction between rotors operating near each other. Brushless motors were also tested systematically and characterized by their torque, rpm, and efficiency. It was found that the maximum efficiency of the motors tested was only 60%, which has significant effects on the efficiency of the coupled system. A method for rotor and motor coupling was also established that utilized the motor efficiency curves and the known torque and rotational speed of the rotors at their operating thrust. Through this, it was found that propulsion system efficiency could be increased by 10% by simply using the proper motor and rotor combination. Further, coupled design would have additional benefits and could increase vehicle efficiency further.